HEC-RAS

I am currently reviewing a HEC-RAS model completed a couple of years ago. It was created with version 2.1 and I am using 2.2. I have two models with different storage alternatives. One of the models works with 2.2 while the others freezes up soon after start-up. I am not sure of the compatibility of version 2.1 and 2.2. Also, I have come across several ineffective flow areas throughout the model and I was wondering if someone could shed some light onto some common reasons that ineffective flow areas would be used, possibly blockage of the river or negligible flow velocities?

Jamie Brescol
McNamee, Porter, & Seeley

Ineffective flow areas are typically applied to bridge/culvert inlets and outlets to define ponding areas outside of the flow path to the right and left of the openings. They will also have an elevation associated with them that typically represents an overtopping elevation for the roadway. Upstream water surface elevations above the level of the roadway would place the ponding areas back into the primary flood flow path as part of the weir overflow. They are also used to define overbank areas which are outside of the primary flood flow path and represent backwater ponding areas.

I don't know about the compatibility of the two versions but I have not experienced any problems to date.

Charles D. Absher, PE
Jordan, Jones & Goulding, Inc.

The two most common reasons that I use ineffective flow areas for are;

1)Expansion and contraction (typically at road crossings) areas. See the (FHWA) WSPRO or RAS User's manual for a description.

2) Cross sections that have banks higher than the floodplain (or a levee). If you don't set the ineffective flow area at the top of the banks, then any elevation that is higher than the floodplain will convey water in the floodplain - even if it didn't get high enough to go over the banks and down into the floodplain.

Charles A. also had some good examples using bridges.

-Dave Briglio
Wiedeman and Singleton, Inc.